Area Forecast Discussion

WHAT HAS CHANGED

Severe thunderstorm watch has been issued for a majority of the region mainly for the wind threat.

KEY MESSAGES

1) Potential for severe weather exists today and Friday, but large uncertainty exists in timing/coverage/threats

2) Low probability flash flooding concerns exists through Friday due to warm, moist environment

3) Above-average temperature with potential for record high minimums possible through Friday, pending storm outcomes

DISCUSSION

KEY MESSAGE 1... The warm, humid environment will continue into Friday, keeping chances for showers and thunderstorms in the forecast. Additional thunderstorms are expected Friday in advance of a cold front and crossing upper trough. A brief period of dry weather and more seasonable temperature will follow.

High SBCAPE/DCAPE values and meager shear should support storms capable of damaging wind gusts, however, there is looking to be a slight increase in probability for large hail. Most of the area is now in a Slight (2/5) risk for severe weather (mainly for wind).

Friday features a more well defined mid-level shortwave and surface frontal boundary that offers a lifting mechanism. This could result in more bullish precipitation/severe chances with the afternoon passage.

KEY MESSAGE 2... Despite fluctuations in mid-level moisture content, area PWAT values will remain in the 90th and higher percentile ranges through Friday while thermal profiles remain warm. These factors alone create non-zero flash flood risks as they favor warm-rain processes that result in higher and more efficient rainfall rates. Add in generally weaker mid-level flow (though storm motion quickens Friday), the risk for flash flooding exists each day.

However, fairly dry surfaces dampens the likelihood of flash flooding actually developing for any of these periods. The most likely outcome is minimal flooding occurrences, with issues only developing in poor-drainage locations that see prolonged 1-2"/hr rates or areas that happen to see multiple rounds of these efficient rains in a short amount of time.

KEY MESSAGE 3... The combination of area dew points remaining in the 60s overnight/70s during the day while seeing enough periods of sunshine means increased heat concerns today into Friday morning, with impacts more acutely impacting heat-sensitive populations within urban environments. A brief hour of heat indices near 100F can't be ruled out, however, this is unlikely to be prolonged enough for headline issuance. Even still the lack of significant overnight cooling can act to exasperate any heat-related impacts until a cooler airmass arrives Friday night into Saturday morning.

The biggest caveat to this heat potential is that convective activity could act to limit diurnal heating (or further limit overnight cooling) if it results in rain over a given location and/or maintains thicker cloud cover than anticipated.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Weak surface convergence along a wind/temperature gradient in eastern OH plus a weak vortex traversing Lake Erie is providing lift within the unstable environment for at least scattered thunderstorm development through 00z today. Areal coverage at TAF onset time favors near ZZV/FKL/DUJ before migrating ESE through PIT/LBE/MGW (among all other terminals) and then tapering off/exiting east near/after 00z. Any thunderstorm will be capable of heavy rain reducing visibilities to 2 miles or less, gusty and erratic wind, and potential for short-notice storm development if/when outflows collide.

VFR overnight will see increasing moisture convergence ahead of the approaching shortwave/surface front, resulting in MVFR to locally IFR cigs for most terminals between 07z-15z. Though unlikely to occur, one component to monitor is how far east a MCS cluster persists during the overnight period as it leaves the lower OH River Valley; if it sustains longer than modeled, thunderstorms could reach ZZV (or even HLG) between 06z-10z. This could impact components like ceiling restrictions and future convective develop for Friday.

Outlook... Confidence remains low in the coverage and location on new storm development Friday along/ahead of a passing upper shortwave and surface cold front. Any thunderstorm that develops likely favors IFR visibilities, MVFR cigs and brief gusty wind.

Dry advection and subsidence in the post-frontal environment favors VFR Friday evening into Saturday. The next precipitation chance arrives with shortwave movement Sunday.

PBZ WATCHES / WARNINGS / ADVISORIES

PA...None. OH...None. WV...None.